The metazoan has evolved various defensive mechanisms to protect itself against the detrimental consequences of stress. Many of the stress responsive mechanisms require altering the composition of their proteomes, a remodeling that may either become lost or exacerbated during the course of aging. This remodeling often includes enhancing the networks of stress responsive proteins and chaperones, many of which are targeted for specific subcellular compartments or organelles, including mitochondria. Though possessing an isolated genome, mitochondria have a proteome that is predominantly composed of proteins encoded in the nucleus and translated in the cytoplasm. A mitochondrial targeting sequence (MTS) is required on the majority of mitochondrial proteins to drive their import into mitochondria. The decision as to whether a protein becomes translocated or not is often contained within the targeting sequence of the protein itself. Surprisingly, a large percentage of proteins that contain an MTS sequence are predicted as dually localized in other subcellular compartments as well. Notably, a number of dually localized proteins are actually mitochondrial stress responsive proteins or chaperones. We hypothesize that 1) the dual localization of a subset of mitochondrial proteins allows for an adaptive plasticity in the composition of the mitochondrial proteome, and 2) the specific MTS of a stress-responsive protein will bias the efficiency of its import toward populations of aged mitochondria. In this project, the nematode C. elegans will be used to investigate these hypotheses. In this proposal, we will undertake a series of methods to both understand how dually targeted proteins fluctuate between subcellular compartments across the lifespan of an organism, and how the targeting signal serves as an active mechanism by which the import and localization of these proteins are regulated.